The patch titled
clocksource: introduce CLOCK_MONOTONIC_RAW
has been removed from the -mm tree. Its filename was
clocksource-introduce-clock_monotonic_raw.patch
This patch was dropped because an updated version will be merged
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: clocksource: introduce CLOCK_MONOTONIC_RAW
From: john stultz <johnstul@xxxxxxxxxx>
In talking with Josip Loncaric, and his work on clock synchronization (see
btime.sf.net), he mentioned that for really close synchronization, it is
useful to have access to "hardware time", that is a notion of time that is not
in any way adjusted by the clock slewing done to keep close time sync.
Part of the issue is if we are using the kernel's ntp adjusted representation
of time in order to measure how we should correct time, we can run into what
Paul McKenney aptly described as "Painting a road using the lines we're
painting as the guide".
I had been thinking of a similar problem, and was trying to come up with a way
to give users access to a purely hardware based time representation that
avoided users having to know the underlying frequency and mask values needed
to deal with the wide variety of possible underlying hardware counters.
My solution is to introduce CLOCK_MONOTONIC_RAW. This exposes a nanosecond
based time value, that increments starting at bootup and has no frequency
adjustments made to it what so ever.
The time is accessed from userspace via the posix_clock_gettime() syscall,
passing CLOCK_MONOTONIC_RAW as the clock_id.
Signed-off-by: John Stultz <johnstul@xxxxxxxxxx>
Cc: Roman Zippel <zippel@xxxxxxxxxxxxxx>
Cc: Josip Loncaric <use-math@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/clocksource.h | 3 ++
include/linux/time.h | 2 +
kernel/posix-timers.c | 15 ++++++++++
kernel/time/timekeeping.c | 49 ++++++++++++++++++++++++++++++++++
4 files changed, 69 insertions(+)
diff -puN include/linux/clocksource.h~clocksource-introduce-clock_monotonic_raw include/linux/clocksource.h
--- a/include/linux/clocksource.h~clocksource-introduce-clock_monotonic_raw
+++ a/include/linux/clocksource.h
@@ -79,6 +79,7 @@ struct clocksource {
/* timekeeping specific data, ignore */
cycle_t cycle_interval;
u64 xtime_interval;
+ u64 raw_interval;
/*
* Second part is written at each timer interrupt
* Keep it in a different cache line to dirty no
@@ -86,6 +87,7 @@ struct clocksource {
*/
cycle_t cycle_last ____cacheline_aligned_in_smp;
u64 xtime_nsec;
+ u64 raw_snsec;
s64 error;
#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
@@ -215,6 +217,7 @@ static inline void clocksource_calculate
/* Go back from cycles -> shifted ns, this time use ntp adjused mult */
c->xtime_interval = (u64)c->cycle_interval * c->mult;
+ c->raw_interval = (u64)c->cycle_interval * c->mult_orig;
}
diff -puN include/linux/time.h~clocksource-introduce-clock_monotonic_raw include/linux/time.h
--- a/include/linux/time.h~clocksource-introduce-clock_monotonic_raw
+++ a/include/linux/time.h
@@ -116,6 +116,7 @@ extern int do_setitimer(int which, struc
extern unsigned int alarm_setitimer(unsigned int seconds);
extern int do_getitimer(int which, struct itimerval *value);
extern void getnstimeofday(struct timespec *tv);
+extern void getrawmonotonic(struct timespec *ts);
extern void getboottime(struct timespec *ts);
extern void monotonic_to_bootbased(struct timespec *ts);
@@ -218,6 +219,7 @@ struct itimerval {
#define CLOCK_MONOTONIC 1
#define CLOCK_PROCESS_CPUTIME_ID 2
#define CLOCK_THREAD_CPUTIME_ID 3
+#define CLOCK_MONOTONIC_RAW 4
/*
* The IDs of various hardware clocks:
diff -puN kernel/posix-timers.c~clocksource-introduce-clock_monotonic_raw kernel/posix-timers.c
--- a/kernel/posix-timers.c~clocksource-introduce-clock_monotonic_raw
+++ a/kernel/posix-timers.c
@@ -224,6 +224,15 @@ static int posix_ktime_get_ts(clockid_t
}
/*
+ * Get monotonic time for posix timers
+ */
+static int posix_get_monotonic_raw(clockid_t which_clock, struct timespec *tp)
+{
+ getrawmonotonic(tp);
+ return 0;
+}
+
+/*
* Initialize everything, well, just everything in Posix clocks/timers ;)
*/
static __init int init_posix_timers(void)
@@ -236,9 +245,15 @@ static __init int init_posix_timers(void
.clock_get = posix_ktime_get_ts,
.clock_set = do_posix_clock_nosettime,
};
+ struct k_clock clock_monotonic_raw = {
+ .clock_getres = hrtimer_get_res,
+ .clock_get = posix_get_monotonic_raw,
+ .clock_set = do_posix_clock_nosettime,
+ };
register_posix_clock(CLOCK_REALTIME, &clock_realtime);
register_posix_clock(CLOCK_MONOTONIC, &clock_monotonic);
+ register_posix_clock(CLOCK_MONOTONIC_RAW, &clock_monotonic_raw);
posix_timers_cache = kmem_cache_create("posix_timers_cache",
sizeof (struct k_itimer), 0, SLAB_PANIC,
diff -puN kernel/time/timekeeping.c~clocksource-introduce-clock_monotonic_raw kernel/time/timekeeping.c
--- a/kernel/time/timekeeping.c~clocksource-introduce-clock_monotonic_raw
+++ a/kernel/time/timekeeping.c
@@ -44,6 +44,7 @@ __cacheline_aligned_in_smp DEFINE_SEQLOC
*/
struct timespec xtime __attribute__ ((aligned (16)));
struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
+struct timespec monotonic_raw;
static unsigned long total_sleep_time; /* seconds */
static struct timespec xtime_cache __attribute__ ((aligned (16)));
@@ -106,6 +107,39 @@ void getnstimeofday(struct timespec *ts)
EXPORT_SYMBOL(getnstimeofday);
/**
+ * getrawmonotonic - Returns the raw monotonic time in a timespec
+ * @ts: pointer to the timespec to be set
+ *
+ * Returns the raw monotonic time (completely un-modified by ntp)
+ */
+void getrawmonotonic(struct timespec *ts)
+{
+ unsigned long seq;
+ s64 nsecs;
+ cycle_t cycle_now, cycle_delta;
+
+ do {
+ seq = read_seqbegin(&xtime_lock);
+
+ /* read clocksource: */
+ cycle_now = clocksource_read(clock);
+
+ /* calculate the delta since the last update_wall_time: */
+ cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
+
+ /* convert to nanoseconds: */
+ nsecs = ((s64)cycle_delta * clock->mult_orig) >> clock->shift;
+
+ *ts = monotonic_raw;
+
+ } while (read_seqretry(&xtime_lock, seq));
+
+ timespec_add_ns(ts, nsecs);
+}
+
+EXPORT_SYMBOL(getrawmonotonic);
+
+/**
* do_gettimeofday - Returns the time of day in a timeval
* @tv: pointer to the timeval to be set
*
@@ -187,6 +221,7 @@ static void change_clocksource(void)
clock->error = 0;
clock->xtime_nsec = 0;
+ clock->raw_snsec = 0;
clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
tick_clock_notify();
@@ -255,6 +290,8 @@ void __init timekeeping_init(void)
xtime.tv_nsec = 0;
set_normalized_timespec(&wall_to_monotonic,
-xtime.tv_sec, -xtime.tv_nsec);
+ set_normalized_timespec(&monotonic_raw, 0,0);
+
update_xtime_cache(0);
total_sleep_time = 0;
write_sequnlock_irqrestore(&xtime_lock, flags);
@@ -453,6 +490,7 @@ void update_wall_time(void)
offset = clock->cycle_interval;
#endif
clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift;
+ clock->raw_snsec += (s64) monotonic_raw.tv_nsec << clock->shift;
/* normally this loop will run just once, however in the
* case of lost or late ticks, it will accumulate correctly.
@@ -460,6 +498,7 @@ void update_wall_time(void)
while (offset >= clock->cycle_interval) {
/* accumulate one interval */
clock->xtime_nsec += clock->xtime_interval;
+ clock->raw_snsec += clock->raw_interval;
clock->cycle_last += clock->cycle_interval;
offset -= clock->cycle_interval;
@@ -469,6 +508,11 @@ void update_wall_time(void)
second_overflow();
}
+ if (clock->raw_snsec >= (u64)NSEC_PER_SEC << clock->shift) {
+ clock->raw_snsec -= (u64)NSEC_PER_SEC << clock->shift;
+ monotonic_raw.tv_sec++;
+ }
+
/* accumulate error between NTP and clock interval */
clock->error += tick_length;
clock->error -= clock->xtime_interval << (NTP_SCALE_SHIFT - clock->shift);
@@ -481,6 +525,11 @@ void update_wall_time(void)
xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift;
clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
+ /* store full nanoseconds into raw_monotonic */
+ monotonic_raw.tv_nsec = (s64)clock->raw_snsec >> clock->shift;
+ clock->raw_snsec -= (s64)monotonic_raw.tv_nsec << clock->shift;
+
+
update_xtime_cache(cyc2ns(clock, offset));
/* check to see if there is a new clocksource to use */
_
Patches currently in -mm which might be from johnstul@xxxxxxxxxx are
proper-extern-for-late_time_init.patch
introduce-explicit-signed-unsigned-64bit-divide.patch
convert-a-few-do_div-user.patch
remove-div_long_long_rem.patch
ntp-cleanup-ntpc.patch
ntp-ntp4-user-space-bits-update.patch
ntp-increase-time_freq-resolution.patch
ntp-increase-time_offset-resolution.patch
ntp-support-for-tai.patch
ntp-rename-tick_length_shift-to-ntp_scale_shift.patch
ntp-remove-current_tick_length.patch
ntp-handle-leap-second-via-timer.patch
clocksource-introduce-clock_monotonic_raw.patch
clocksource-introduce-clock_monotonic_raw-fix.patch
clocksource-introduce-clock_monotonic_raw-fix-checkpatch-fixes.patch
clocksource-introduce-clocksource_forward_now.patch
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